The general design of hydrostatic drive systems for vehicles such as self-propelled mowers and lawn or garden tractors, is known. Integrated hydraulic transmissions in which the pump and motor are enclosed in the same housing and share a common sump and center section have become quite popular. Under certain circumstances, a vehicle manufacturer may be willing to sacrifice the convenience and cost savings offered by an integrated design for the flexibility and easy maintenance offered by separate, but connected hydraulic pumps and motors.
Hydraulic pump and motor combinations without brackets are also known, but these designs are not modular in that the pumps and motors are integrally connected in some fashion, share housings, or are separately connected to a vehicle frame.
Hydraulic pump and motor modules having an end-to-end pump-and-motor design and differential gearing are described in U.S. Pat. Nos. 6,705,840, 7,056,101, and 7,640,738. These designs show multiple pumps and motor in a single module which limits the flexibility of this modular design for a given vehicle design. Thus, an alternative transmission assembly design would be useful to vehicle manufacturers.